Our body burns, or metabolizes, food to produce energy in the form of heat. This heat warms our body and powers every move we make. The amount of heat produced by metabolizing food is measured in units called kilocalories.
A kilocalorie is the amount of energy required to raise the temperature of 1 kilogram of water, 1 degree Celsius.
How much energy do different food types contain? 1 gram measures:
- Protein: 4 calories.
- Carbohydrates: 4 calories.
- Alcohol: 7 calories.
- Fat: 9 calories.
Interesting, right? Protein and carbohydrates have less than half the energy content of fat.
All food provides calories. All calories provide energy. However, there is food with “empty calories”, meaning calories with no extra benefits, i.e. no nutrients such as amino acids, vitamins, dietary fiber or minerals. Empty calories are also called discretionary calories.
Examples of foods with empty calories are for instance table sugar and ethanol, i.e. the kind of alcohol found in beer, wine and spirits. On their own, these foods provide energy, but no nutrients.
Every Calorie Counts
All calories, regardless of where they come from, provide energy. If we bring in more calories/energy than we spend each day, we gain weight. If we take in fewer calories than are used up, we lose weight.
How Many Calories do we Need?
The amount of energy that is used each day could be divided in two parts:
1. Resting Energy Expenditure
The energy needed when the body is at rest, i.e. the energy spent if we were to stay in bed all day. This energy is called resting energy expenditure (REE). The REE accounts for 60 to 70 percent of all energy needed each day. Use the table below to find your REE.
2. Energy Used for Physical Work
The other large part of energy use is that for physical activity during the day – from brushing teeth, walking from the bus, to working out in the gym. The table below provides an indication of how many calories that are used during an hour of different kinds of activities.
Lose 1K of Body Fat
1,000 grams or 1 kg or slightly more than 2 lbs equals roughly 7,000 food calories, i.e. it takes 7,000 calories to gain or lose 1 kg of body fat.
- Decrease the food consumption from 2,400 calories a day to 1,900 and continue doing the same physical work leads to losing 1 kg of fat after 14 days.
- Going the other way, increasing the food consumption from 1,900 calories a day to 2,400 and continue doing the same physical work leads to gaining 1 kg of fat after 14 days.
Because lean body mass is lost along with body fat, the exact figure depends on the initial body fat percentage. The amount of lean body mass a person will lose is based on the initial body fat level and size of the daily calorie deficit. Lean people tend to lose more lean body mass and keep more fat. Obese/overweight persons lose more body fat and retain more lean tissue.